Articles

Mining projects are applying the age-old notion of "check your work" against comminution circuit design, mill power requirement estimates and mill throughput estimates. The best way to test the results of one comminution modelling system is to replicate the calculation in a different modelling system. Unfortunately, the most common comminution modelling systems require largely incompatible test programs to provide input parameters. This paper presents some example protocols for sample collection and preparation from drillcore that simultaneously returns comminution datasets suitable for a Bond Work Index based method, an Axb dataset, and a set of SPI results. By carefully collecting data for all three methods, high quality geometallurgical dataset can be created.
(Presented at Procemin 2008, Santiago, Chile)[↑ read less ↑]

Comminution tests on a particular project have displayed completely different breakage characteristics relative to a database, depending upon which test procedure was performed. Some of these differences are attributed to the dimensions of the sample that is presented to a test, e.g., a Bond crushing test compared to a ball mill test, while other differences can be attributed to a hardness profile that is inherent in a particular size class compared to another coarser or finer size class, e.g., fracture density and mineral filling and/or grain size. Ore types can respond with a characteristic hardness profile by size which may not be identified if only one sampling and testwork regime is used.
(Presented at Procemin 2009, Santiago, Chile)[↑ read less ↑]

Comminution tests on a particular project have displayed completely different breakage characteristics relativ...[↓ read more ↓]

Unconfined Compressive Strength (UCS) is a commonly used rockmass strength measurement used by rock mechanics practitioners. This paper examines potential relationships between UCS and Bond Work Index values (crushing, rod mill and ball mill). Data from 11 mines located around the world is analysed for correlations between UCS and various Wi values.[↑ read less ↑]

Unconfined Compressive Strength (UCS) is a commonly used rockmass strength measurement used by rock mechanics ...[↓ read more ↓]

The Bond low energy impact (crushing) work index test is specified to be performed on rock specimens between 50 mm and 75 mm in effective diameter. NQ-diameter drill core, frequently used in mineral exploration programs does not meet that specification, it being 45 mm diameter or less.

This paper reports the effect of performing the impact test on contiguous sections of HQ diameter and NQ diameter core, exploring the hypothesis that the contiguous intervals give equivalent results in spite of the core diameter difference.[↑ read less ↑]

The Bond low energy impact (crushing) work index test is specified to be performed on rock specimens between 5...[↓ read more ↓]

Blank spreadsheet that is pre-populated with the field names needed to import laboratory test results into the SAGMILLING.COM circuit model testwork database (subscription required).

Enter your test results, one per row, arranged into the columns indicated.

To import into your testwork database, copy the block of cells starting with the top row down to the bottom of your data. Paste this block into the import field in the website "add testwork" page (do not worry if the text looks scrambled, the website can understand it).[↑ read less ↑]

Blank spreadsheet that is pre-populated with the field names needed to import laboratory test results into the...[↓ read more ↓]

The drop weight test is a common laboratory measurement used to determine the comminution characteristics of rock samples. A common metric derived from a drop weight test is a value "A×b". Another common metric that is derived from the SMC Test™ variant of a drop weight test is a "Drop Weight Index", abbreviated as DWi. This work looks at a public database of test results to determine a relationship for DWi as a function of A×b.[↑ read less ↑]

The drop weight test is a common laboratory measurement used to determine the comminution characteristics of r...[↓ read more ↓]

The Bond "Third Theory" of comminution was originally divided into three size classes reflecting the varieties of comminution equipment common during the time period when Bond (and his collaborators) were gathering the information to calibrate comminution models. The middle size class, represented by rod milling, is fitted to a tumbling test, referred to as the Bond rod mill work index (Wi RM , or RWi).
The apparatus used to determine this work index was described in 1943 by Bond & Maxton. Unfortunately, there are some laboratories that have deviated from the apparatus specified by Bond & Maxton and there are modern comminution models that are calibrated to this non-standard mill geometry. (document revised 2016-04-27)[↑ read less ↑]

The Bond "Third Theory" of comminution was originally divided into three size classes reflecting the varieties...[↓ read more ↓]

Spreadsheet that accompanies the Procemin 2016 paper by Alex Doll. This spreadsheet contains a database of public grindability testwork for projects worldwide. The data is collected mostly from conference papers and NI 43-101 reports. The NI 43-101 data may not be used for commercial purposes (hence it is being given away); but it may be used for research purposes such as model calibrations and project benchmarking.[↑ read less ↑]

Spreadsheet that accompanies the Procemin 2016 paper by Alex Doll. This spreadsheet contains a database of pu...[↓ read more ↓]

This work presents a public database of over 800 grindability measurements and a set of equations for converting between different grindability tests based on this database. Several laboratory grindability measurements commonly used in the mining industry; each is generally applicable to a particular grindability model and is incompatible with other models. Conversion between different test types is possible using a series of empirical relationships between those tests conducted at similar size classes.
The commonly used grindability tests included in the database are the Bond work indices for ball milling, rod milling and crushing; the drop weight test results A, b, A×b, DWi, Mia, Mic, Mih and ta; SAG grindability index, SGI or SPI™; and other values such as Mib and point load index.
Some examples of power-based model specific energy predictions will be compared to published mill surveys to observe how well the different models predict the specific energy of an industrial mill.[↑ read less ↑]

This work presents a public database of over 800 grindability measurements and a set of equations for converti...[↓ read more ↓]

Review of the JKMRC Mineral Comminution Circuits textbook (Reference 1), and discussions with practitioners of the JKSimMet software have led to the following simplified description of the opera- tion of the JK method for modelling a ball mill. A scenario of scaling up a pilot plant test to a full sized circuit is assumed in this discussion.[↑ read less ↑]

Multi-stage crushing plants, including high pressure grinding roll (HPGR) circuits, require more materials handling equipment than SAG and ball mill circuits. A temptation exists to neglect the energy consumption of materials handling when doing desktop comparisons of HPGR versus SAG milling circuits because estimation of materials handling power requirements can demand significant general arrangement drafting that is not available when performing preliminary scoping or "desktop" studies.

The largest component of materials handling power is consumed by conveyors when lifting material between stages of crushing, meaning that a simple potential energy model can be used to evaluate conveying specific power consumption. This potential energy consumption for conveying can then be factored to provide overall materials handling specific energy consumption suitable for desktop studies of HPGR and other multi-stage crushing circuits. The technique also permits different crushing circuit flowsheets to be evaluated, at a preliminary level, by simply counting the number of times a conveyor must "lift" ore from ground level up to a bin or other equipment mounted up high.
(Presented at CMP 2015, Ottawa, Canada; represented as a poster at Procemin 2015, Santiago, Chile)[↑ read less ↑]

This LibreOffice spreadsheet contains the raw data used to create Table 1 and Table 2 of the paper "An updated data set for SAG mill power model calibration", presented at IMPC 2016 in Quebec City, Canada in September, 2016. Refer to the paper for the definitions and meanings of the different columns.

The file format should be completely compatible with OpenOffice software, and mostly compatible with Microsoft Excel (the charts will probably not work in Excel).[↑ read less ↑]

This LibreOffice spreadsheet contains the raw data used to create Table 1 and Table 2 of the paper "An updated...[↓ read more ↓]

This paper expands the SAG mill survey database published by the Author at Procemin 2013. The new database includes 49 published SAG/AG mill surveys and includes mills from all over the world. The paper will compare the survey database to SAG mill models by Austin, Morrell and Hogg & Fuerstenau with the purpose of demonstrating the degree of fit of the models to surveys and validating any empirical “fitting factors” used in the models.

SAG mill power draw models are used in mill design and grinding circuit modelling to predict how much power will be consumed by a particular mill geometry and operating configuration. The importance of conducting surveys suited to model calibration will be highlighted because the review of literature shows that survey information important to modelling is often missing or omitted. A recommendation for the collection of data during a mill survey is presented, along with some assumptions used by the Author in the absence of certain data. The benefit to mining companies of publishing their survey data, and thereby allowing modellers to improve their model calibration, is discussed.

The comparison of models requires a discussion of the measurement of power in a mill drive system as the models use slightly different position in the electrical network for "where power is measured". The benchmarking of models against plant operations requires a similar discussion of power measurement. (paper published at IMPC 2016)[↑ read less ↑]

This paper expands the SAG mill survey database published by the Author at Procemin 2013. The new database in...[↓ read more ↓]

Many power-based grinding models exist, and most operators are familiar with Fred Bond's "third theory". Bond's model is most commonly used to describe primary and secondary grinding to product sizes above, for example, 100 μm. Operators sometimes use Bond's equation to describe grinding in situations where it is not appropriate, such as fine grinding below 50 μm. Using an alternative model would be a better choice in this situation.[↑ read less ↑]

Paper presented at CMP 2017.
Many power-based grinding models exist, and most operators are familiar with ...[↓ read more ↓]

Comminution circuit design and geometallurgy is normally performed using the power-based class of models. Many models of this type exist and all of them are empirically based, meaning they are calibrated to fit a specific set of laboratory results to a database of mill surveys. Most empirical comminution models are calibrated to two-stage AG/SAG mill and ball mill circuits -- this work compares the performance of several commonly used power-based models to surveys conducted on single-stage AG/SAG circuits.

Survey data was collected from Anglo American’s El Soldado mine and from published works by others and the operating specific energy consumption of circuit was computed. Ore grindability measurements were collected, allowing model predictions of specific energy consumption to be computed using models proposed by Jorquera & Becerra (at El Soldado), Morrell, Barratt and Amelunxen. The actual operating specific energy consumption is finally compared to the
predictions.

The more complex ores required more complex models to obtain reliable predictions; whereas, the simple ores can be modelled by any of the models. A complex ore, such as Palabora, requires grindabililty measurements be made at three size classes, such as the three Bond work indices. A simple ore, such as El Soldado, can be reliably modelled with a single grindabily measurement, such as the SAG Grindability Index. A quick diagnostic of whether an ore is “complex” or “simple” is to compare the three Bond work indices: “simple” ores generally have the same value for all
three work index values, whereas “complex” have dramatically different values for all three.[↑ read less ↑]

Paper presented at Procemin 2017.
Comminution circuit design and geometallurgy is normally performed using ...[↓ read more ↓]

Matrix Algebra, also known as linear algebra, is well suited to solving material balance problems encountered in plant design and optimisation. A properly constructed matrix is not sensitive the iterations of circular calculations that can cause 'hard wired' spreadsheet mass balances to fail to properly converge and balance. This paper demonstrates how to construct equations and use matrix algebra on a typical computer spreadsheet to solve an example mass balance during a mineral processing plant design.[↑ read less ↑]

Matrix Algebra, also known as linear algebra, is well suited to solving material balance problems encountered ...[↓ read more ↓]

Computerized spreadsheets are a commonly used tool in the engineering industry. Unfortunately, they are a very generic tool, and do require care when used to perform process engineering calculations. This paper describes many tools and tricks developed in the consulting engineering industry to make calculations more readable and to perform quality assurance.[↑ read less ↑]

Computerized spreadsheets are a commonly used tool in the engineering industry. Unfortunately, they are a very...[↓ read more ↓]

Grinding circuit power is commonly used as a defining parameter in circuit design and analysis. However, the circuit power can be defined at a number of points, and depending upon the use of the power, different system losses must be applied to the power reported. Further, different comminution models report power measured at different locations.[↑ read less ↑]

Grinding circuit power is commonly used as a defining parameter in circuit design and analysis. However, the c...[↓ read more ↓]

Slide presentation providing an overview of the process for selection motors for grinding mills. Motors are selected based on "mill overload" conditions that are more rigorous than the mill process conditions.
(Presented at Procemin 2010, Santiago, Chile)[↑ read less ↑]

Slide presentation providing an overview of the process for selection motors for grinding mills. Motors are se...[↓ read more ↓]

Many grinding mill owners choose a variable speed drive for their mill to cope with variations in ore hardness, plant throughput and other process considerations. Two important engineering decisions that owners must make before purchasing a variable speed drive system are the selection of the motor nominal design speed and the motor maximum speed.

The owner's choice of the knee point (motor rated speed) coupled with the owner's choice of the motor rated power define the rated torque of a motor. The electrical designers of motors use this rated torque to fix the size of the motor components. The price of a motor depends on the rated torque of the motor (more-so than the motor rated power and diameter), so for large mills a slight increase of the motor rated speed can result in substantial price savings. Operating at higher mill speeds can reduce operating costs by permitting operation at lower ball charges for a given mill power draw.
(Presented at SAG 2015, Vancouver, Canada)[↑ read less ↑]

Many grinding mill owners choose a variable speed drive for their mill to cope with variations in ore hardness...[↓ read more ↓]

The Bond low energy impact (crushing) work index test is specified to be performed on rock specimens between 50 mm and 75 mm in effective diameter. NQ-diameter drill core, frequently used in mineral exploration programs does not meet that specification, it being 45 mm diameter or less.

This paper reports the effect of performing the impact test on contiguous sections of HQ diameter and NQ diameter core, exploring the hypothesis that the contiguous intervals give equivalent results in spite of the core diameter difference.[↑ read less ↑]

The Bond low energy impact (crushing) work index test is specified to be performed on rock specimens between 5...[↓ read more ↓]

Speaker slides from presentation made at the Universidad Privada del Norte, Cajamarca, Perú, November 25, 2015.

Topic is geometallurgy and the use of process model parameters integrated into a mine production block model to improve the forecasting of production, optimize pit designs, and permit the calculation of profit by block (instead of using a single cut-off grade).[↑ read less ↑]

Speaker slides from presentation made at the Universidad Privada del Norte, Cajamarca, Perú, November 25, 201...[↓ read more ↓]